(1) Field of the Invention
The present invention relates to a fuel evaporation gas treating device wherein a passage communicated with a canister port facing a bore of a carburetor provided to an engine mounted on a vehicle is connected with a canister incorporating an activated carbon layer, while another passage from a fuel system is communicated with the activated carbon layer. More particularly, the invention pertains to a fuel evaporation gas treating device arranged such that the first-mentioned passage is provided with a solenoid-operated changeover valve with an atmospheric air vent provided with a filter, and a heat-sensitive means connected with the changeover valve for actuating two kinds of bimetal in order to enable the changeover valve to operate, thereby allowing the changeover valve to selectively connect the canister and the atmospheric air vent with each other.
(2) Description of the Prior Art
It is well known that in an engine mounted on an automobile, as shown in FIG. 1, a fuel 28 stored in a fuel system, e.g., a fuel tank 16 evaporates at all times, and the fuel having evaporated, i.e., what is called evaporation gas, floats in the tank 16, filling the same.
Accordingly, such a device has been generally and widely employed for preventing the evaporation gas from being released into the atmospheric air as a canister 14 incorporating an activated carbon layer 13 adapted to temporarily store the evaporation gas and introduce the same into a carburetor 1, when the engine is operated, for burning the evaporation gas.
However, the evaporation gas differs in the evaporation amount according to the change in the ambient temperature of the engine system and the fuel system of the above-mentioned engine and the like. In consequence, there is also an immeasurable change at all times in the amount of the evaporation gas stored in the canister 4.
Therefore, metering of the fuel in the carburetor 1 is conventionally effected such that the set metering value is fitted for the minimum amount of the gas stored in the canister 4 in order to prevent the air-fuel ratio from becoming overly lean and thereby affecting of the stability the engine operation.
There is, however, a problem when the amount of stored gas increases, wherein a larger amount of the evaporation gas is introduced into the carburetor 1, bringing the carburetor 1 into a rich state. Thus, during hot engine operation when the air-fuel mixture is rich, the engine system may become unstable.
Moreover, there is a disadvantage in the cold operation of an engine wherein the introduction of the evaporation gas may cause deterioration of the exhaust emission control.